JPH0814102A - Layer burning type internal combustion engine - Google Patents

Abstract

PURPOSE:To produce a strong tumbling flow by preventing reduction in the flow rate coefficient of an intake main flow. CONSTITUTION:An intake main flow F is caused to gradually flow to an outer half side by means of action of a centrifugal force when it reaches an upstream bent part 51 after flowing into an intake manifold 3. However, since the cross section of the upstream bent part smoothly changes from a complete circle to a regular trapezoidal form, the intake main flow F flows without any resistance and no reduction in the flow rate coefficient occurs. When the intake main flow F transfers to a downstream bent part 52, it is caused to gradually flow to an outer half side thereof. However, since the cross section of the downstream bent part smoothly changes from a regular trapezoidal form to an inverted trapezoidal form, the intake main flow F flows without any resistance and no reduction occurs in the flow rate coefficient.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stratified combustion internal combustion engine, and more particularly to a technique for generating a strong tumble flow in a combustion chamber.

[0002]

2. Description of the Related Art In recent years, in gasoline engines for automobiles and the like, in order to reduce harmful exhaust gas components such as HC and CO and improve fuel efficiency, the air-fuel ratio of the air-fuel mixture is changed to the theoretical air-fuel ratio (14.7).
A much leaner lean burn engine has been proposed. As a lean-burn engine, a lean air-fuel mixture is ignited by generating a lean air-fuel mixture layer (rich layer) and a thin air-fuel mixture layer (lean layer) in the combustion chamber and igniting the rich layer. The enabling stratified combustion engine is promising. Then, in order to generate a rich layer and a lean layer in the combustion chamber, a vertical vortex (Vertical V
Ortex), that is, a stratified combustion engine using a tumble flow has already been put into practical use.

26 and 27 schematically show the main parts of an example of a stratified combustion engine of this type. As shown in the figure, this engine has a pent roof type combustion chamber 104 defined by an intake side slope 102 and an exhaust side slope 103 formed in a cylinder head 101, and further the combustion chamber 104. The intake is a two-valve engine in which the intake is performed from a pair of intake ports 105 and 106 that are opened to the intake side slope 102. The fuel injection valve 107 is provided only on one intake port 105, and a relatively rich air-fuel mixture is supplied from the intake port 105 to the combustion chamber 104.
Only the air flows in from the other intake port 106. Further, on the exhaust side slope 103, the fuel injection valve 1
The spark plug 108 is arranged at a position facing the intake port 105 provided with 07, while the other intake port 106 is provided.
The exhaust port 109 is opened at a position opposed to. In the figure, 110 is an intake valve, 111 is an exhaust valve, 112
Is a cylinder bore 1 formed in the cylinder block 113.
It is a piston which moves up and down in the inside of 14.

In this engine, when the piston 112 begins to descend in the intake stroke, a rich air-fuel mixture and air are sucked into the combustion chamber 104 under negative pressure from an intake manifold (not shown) through both intake ports 105 and 106. It The air-fuel mixture and the air that have flowed into each intake port 10
5, 106 flows along the inner wall of the cylinder bore 114 on the extension line of 5, 106, whereby a tumble flow Fm of air-fuel mixture and a tumble flow Fa of air are generated in the combustion chamber 104. When these tumble flows Fm and Fa are preserved even in the compression stroke, the tumble flow Fm of the air-fuel mixture forming the rich layer flows around the spark plug 108, and good ignition is obtained, and as a whole. Combustion with a lean air-fuel ratio becomes possible. The main constituents of the tumble flows Fm and Fa are the intake flows flowing from the upper portions of the intake ports 105 and 106.

[0005]

In the stratified combustion engine described above, the tumble flow F in the combustion chamber 104 is also increased.
Depending on the strength of m and Fa, lean combustion may not be established. That is, when the tumble flows Fm and Fa are strong, there is almost no flow in the swirling axis direction, and the rich layer and the lean layer are separated by this, but when the tumble flows Fm and Fa are weak, the swirling axis is weak. Flow also occurs in the direction, and the separation of the layers becomes unstable. As a result, during the swirling, the tumble flow Fm of the air-fuel mixture and the tumble flow Fa of the air are gradually mixed with each other and reach the vicinity of the spark plug 108.
The air-fuel ratio exceeds the stable combustion limit and the misfire limit and becomes lean. Therefore, in order to perform reliable stratified combustion, the strong tumble flows Fm and Fa must be generated, and the combustion chamber 1 from the upper portions of the intake ports 105 and 106.
It was necessary to increase both the tumble ratio and the flow coefficient in order to increase the intake flow to 04.

However, the cross section of the conventional intake passage from the intake manifold to the intake port is generally circular or elliptical, and the flow coefficient often decreases depending on the engine type. For example, in a V-type engine,
Generally done from between banks, in this case,
The intake manifold descending vertically is largely curved and then connected to the intake ports formed in the cylinder heads of both banks. At this time, in the curved portion of the manifold, the main part of the intake flow (the main intake flow) flows to the outside (that is, the outer half of the bend) by the centrifugal force, so that if the passage cross section is circular or elliptical, The distribution was not smooth and the flow coefficient was lowered.

The present invention has been made in view of the above situation, and improves the flow coefficient by smoothing the flow of the intake main flow.
An object of the present invention is to provide a stratified combustion internal combustion engine that enables generation of a strong tumble flow.

[0008]

In order to solve this problem, therefore, in an internal combustion engine according to claim 1 of the present invention, in a stratified combustion internal combustion engine provided with an intake passage having a curved portion,
The cross-sectional area of the bending outer half of the curved portion was set larger than that of the inner bending half. According to a second aspect of the present invention, in the internal combustion engine of the first aspect, the plurality of curved portions are formed and communicated with the combustion chamber of the internal combustion engine substantially linearly continuously downstream of the curved portion on the downstream side. Form a straight line part to
Further, the cross-sectional area of one half of the straight portion continuous with the outer half of the curved portion is set larger than the cross-sectional area of the other half continuous with the inner half of the curved portion.

According to a third aspect of the present invention, in the internal combustion engine of the second aspect, the boundary between the curved portion on the downstream side and the straight portion is inside an intake port formed in a cylinder head of the internal combustion engine. Positioned. According to a fourth aspect of the present invention, in the internal combustion engine according to the second or third aspect, the internal combustion engine is a V type having an intake passage between V banks, and the upstream side of the curved portion is the V bank. It was formed along an imaginary plane that divides it into two substantially equal parts.

[0010]

In the internal combustion engine according to claim 1 of the present invention, since the cross-sectional area of the bending outer half portion in the bending portion is set to be larger than the cross-sectional area of the bending inner half portion, the intake main flow that is close to the bending outer half portion by centrifugal force is set. Will be distributed smoothly. Therefore, the reduction of the flow coefficient is prevented and a strong tumble flow is generated.

Further, in the internal combustion engine of claim 2, in the case where the straight line portion communicating with the combustion chamber is continuous downstream of the plurality of bending portions, the cross-sectional area of one half portion of the straight line portion continuous with the outer half portion of the bending portion. Is larger than the cross-sectional area of the other half continuous with the inner half of the curved portion, the main intake air flowing through the outer half of each of the plurality of curved portions smoothly flows into the combustion chamber even in the straight portion. .

Further, in the internal combustion engine of the third aspect, since the boundary between the curved portion and the straight portion on the downstream side is located in the intake port, the internal combustion engine has a small space for the intake manifold such as the V-type engine. However, the curved portion can be provided without difficulty. Further, in the internal combustion engine according to claim 4, in the V-type engine, the curved portion on the upstream side is formed along the virtual plane that divides the V bank into two substantially equal parts, so that the shape of the intake passage can be symmetrical in both banks. It will be possible.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a rear view of a V-type engine adopting the present invention. In the figure, reference numeral 1 indicates the entire engine, and 2 indicates an intake manifold. As shown in this figure, the intake manifold 2 is arranged between the V banks of the engine 1, and the left and right branches 3 and 4 thereof are vertically descending along a virtual plane S that bisects the V bank and are left and right. After being bent, it is connected to the cylinder heads 5 and 6 of the left and right banks. In the figure, 7 is the cylinder head 6 of the right bank
Is a surge chamber installed in the upper part of the, and is connected to the intake manifold 2 via the intake pipe 8. Further, 9 is a piston, which is connected to a crankshaft 11 via a connecting rod 10 and has a cylinder block 12
It moves up and down in the cylinder bore 12a formed in.

FIG. 2 (enlarged perspective view of section II in FIG. 1), FIG.
As shown in FIG. 2 (a view from the arrow III in FIG. 2) and FIG. 4 (a view from the arrow IV in FIG. 2), the engine 1 of this embodiment also has a cylinder head 6 in the same manner as the conventional one described above. Although it has a pentroof type combustion chamber 15 defined by the formed intake side slope 13 and exhaust side slope 14, it is a four valve type having an intake valve 16 and an exhaust valve 17 in pairs. There is.

The cylinder head 6 is formed with an intake port 18 for introducing intake air from the intake manifold 2 into the combustion chamber 15. The intake port 18 branches into left and right intake port portions 19 and 20 in the middle thereof. This is Siamese Port. Further, the intake valves 16 are respectively disposed in the openings of both intake port portions 19 and 20 formed on the intake side slope 13, and are driven by a valve operating mechanism (not shown),
Both the intake port portions 19 and 20 and the combustion chamber 15 are communicated / blocked. In FIG. 3, reference numeral 21 is an intake side valve seat that abuts the intake valve 16 and seals it.

On the other hand, the cylinder head 6 has an exhaust port 22 for exhausting to an exhaust manifold (not shown).
The exhaust port 22 is also a Siamese port in which the left and right exhaust port portions 23 and 24 are integrated in the middle. The exhaust valve 17 is disposed in the openings of both the exhaust port portions 23 and 24 formed on the exhaust side slope 14, and like the intake valve 16,
Both exhaust port portions 2 are driven by a valve operating mechanism (not shown).
3, 24 and the combustion chamber 15 are connected and disconnected. 25 in the figure
Is an exhaust side valve seat that abuts and seals the exhaust valve 17, and 26 and 27 are stem guides that guide the intake and exhaust valves 16 and 17, respectively.

When a virtual plane FC (indicated by a broken line in FIG. 2) which defines the combustion chamber 15 on the intake side and the exhaust side including the cylinder axis LC is set, the intake port portions 19 are naturally provided. , 20 open on the intake side of the virtual plane FC, and both exhaust port portions 23, 24 open on the exhaust side of the virtual plane FC. Further, a spark plug 30 which is a means for igniting an air-fuel mixture is arranged at a substantially central top portion of the combustion chamber 15, while a fuel injection means which is a fuel supply means is provided at an upper center of a downstream end portion of the intake manifold 2. A valve 31 is attached to inject atomized fuel toward the center of the intake port 18.

As shown in FIG. 4, the left and right intake port portions 1
The axes LA and LB of the shafts 9 and 20 are parallel to each other, and the intake air flow also flows into the combustion chamber 15 in parallel and linearly while being branched left and right. In the intake stroke, these intake flows that have flown into the combustion chamber 15 as the piston 9 descends, as shown in FIG. 2, along the lower surface of the cylinder head 6 that forms the combustion chamber ceiling surface, and is exhausted in a virtual plane FC. After flowing to the side, it descends along the inner wall surface on the exhaust side of the cylinder bore 12a. Next, these intake flows flow along the upper surface of the piston 9 toward the intake side, then rise along the inner wall surface of the cylinder bore 12a on the intake side, and join with the flow on the lower surface of the cylinder head 6.
As a result, a vertical vortex of the intake air flow, that is, a tumble is generated in the combustion chamber 15.

On the other hand, the intake port 18 is formed with a pair of partition walls 35 that divide the left and right intake port portions 19, 20 into a central passage 33 and a side passage 34 along the respective axial center lines LA, LB. Has been done. As described above, since the fuel injection valve 31 injects fuel toward the center of the intake port 18, most of the injected fuel is in both intake port portions 1.
It is introduced into the central passage 33 of 9, 20.

By adopting the above configuration, the combustion chamber 1
A tumble flow Fm of a relatively rich air-fuel mixture is introduced into the chamber 5 from the central passage 33, while a tumble flow Fa containing almost no fuel is introduced from both side passages 34. Since these tumble flows Fm and Fa swirl in substantially parallel to each other and in the same direction, they are stored in the combustion chamber 15 even in the compression stroke.

In this embodiment, each constituent element has its own characteristic, as will be described below in order. First, the shape of the top surface of the piston 9 will be described with reference to FIGS. 2, 3, 5, and 6. As shown in these drawings, the top surface 40 of the piston 9 is provided with a raised portion 44 having a vertex on the intake side of the virtual plane FC. Ridge 4
The slope vf1 on the virtual plane FC side of No. 4 is formed so as to smoothly continue to the flat top surface 40. Also raised part 4
The inclined surface vf1 of No. 4 is formed such that the cross section parallel to the virtual plane FC is a straight line parallel to the reference plane of the top surface 34 of the piston 9. That is, the slope vf1 of the raised portion 44 is
In the intake stroke, the tumble flows Fm and Fa are transferred to the piston 9
When the direction is changed from the top surface 44 to the inner surface of the cylinder bore 12a, they are formed so as not to mix with each other and to maintain a clean layered structure.

When the piston 9 is near the top dead center of the compression stroke, the outer slope vf2 of the raised portion 44 cooperates with the ceiling of the combustion chamber 15 to generate the squish SF, and the tumble flows Fm, Fa. It is formed so that a slight disorder occurs in the. Further, a valve recess 45 that prevents interference with the intake valve 16 is provided on the outer slope vf2 of the raised portion 44. Accordingly, even if the intake valve 16 overlaps the exhaust valve 17 and opens at the top dead center, the piston 9 can maintain the top dead center position with a high compression ratio without interfering with the intake valve 16. .

Next, the partition wall 35 formed on the left and right intake port portions 19, 20 will be described. As shown in FIG. 7, the partition wall 35 has its downstream end portion extended to the vicinity of the intake valve 16. To be precise, the intake valve 16 is formed with a predetermined gap so as not to come into contact with the umbrella portion 16a and the valve stem 16b of the intake valve 16 and has no influence on the operation of the intake valve 16. Also, the partition wall 35
Is formed at a position substantially along the axial center lines LA, LB of the left and right intake port portions 19, 20, as described above.
The intake air flowing through both intake port portions 19 and 20 flows into the combustion chamber 15 in a more rectified state.

Further, as shown in FIG. 8, both the upstream side end and the downstream side end of the partition wall 35 are formed in a convex curved surface to improve the effect of rectifying the intake air flow and facilitate the manufacture. Has been planned. That is, since the end portion has the convex curved surface, the fluid resistance of the intake air flow is reduced, while when the intake port 18 is formed in the cylinder head 6 by casting, the mold (core) corresponding to the partition wall 35 is removed. This improves the life of the mold and improves the productivity.

Next, the arrangement of the fuel injection valve 31 and the partition wall 35
The relationship with is explained. As described above, the fuel injection valve 31 is attached to the downstream end of the intake manifold 2 and injects fuel from the upstream side of the intake port 18 toward the center thereof. This fuel injection valve 31 is an independent injection type that injects fuel in accordance with the intake stroke, and as shown in FIG. 8, injects atomized fuel into a fan-shaped range centered on its axis LI. On the other hand, since the left and right intake port portions 19 and 20 branched from the intake port 18 are separated into the central passage 33 and the side passages 34 by the partition wall 35, as shown in FIG. Will be out of the injection range. Therefore, a relatively rich air-fuel mixture flows into the combustion chamber 15 from both central passages 33, while almost only air flows from the left and right side passages.

With the above construction, the intake air is introduced into the combustion chamber 15 in a state in which it is separated into the central air-fuel mixture layer and the left and right air layers and is rectified. And
As shown in FIG. 2, three tumble flows, that is, the tumble flow Fm of the air-fuel mixture flowing in the central portion and the tumble flow Fa of air flowing to the left and right of the air are generated from these intake air. Become.

Next, the relationship between the intake valve 16 and the partition wall 35 will be described. As shown in FIG. 8, in the present embodiment, the intake valve 16 is located on the center line of the left and right partition walls 35 (that is, the axial center lines LA and LB of the left and right intake port portions 19 and 20).
While the axial center of is located, the thickness t of the partition wall 35 is formed smaller than the diameter d of the valve stem 16b. Therefore, the inner surface of the partition wall 35 is biased toward the side passage 34 side with respect to the surface of the valve stem 16b. As a result, the flow of the air-fuel mixture along the inner surface of the partition wall 35 is further shifted to the center side as indicated by an arrow P in the figure, and its diffusion is prevented. Therefore, the density of the tumble flow Fm of the air-fuel mixture in the combustion chamber 15 also increases, and the ignition by the spark plug 30 can be performed more reliably.

Next, sectional shapes of the intake manifold 2 and the intake port 18 will be described with reference to FIGS. 3 and 9 to 16. As shown in FIG. 3, the intake pipe 8 and the combustion chamber 15 are formed by the passage 50 formed in the left branch 3 of the intake manifold 2 (hereinafter simply referred to as the intake manifold) and the intake port 18 of the left bank. An intake passage that communicates with each other is formed. The intake passage includes an upstream curved portion 51 formed on the intake pipe 8 side of the left branch 3, a downstream curved portion 52 continuous from the upstream curved portion 51 from the left branch 3 to the intake port 18, and a downstream curved portion. A straight line portion 53 that connects the intake port 18 and the combustion chamber 15 to each other in a substantially straight line is formed continuously with 52. In FIG. 3, the upstream curved portion 51 is formed clockwise in the intake air flow direction, and the downstream curved portion 52 is also formed counterclockwise.

In the present embodiment, the cross section of the intake passage in the upstream curved portion 51 is shown in FIG. 9 (IX-IX sectional view in FIG. 3), FIG. 10 (XX sectional view in FIG. 3), and FIG. 11 (Fig. 3
XI-XI cross-section) and Figure 12 (XII-XII cross-section in Figure 3), it smoothly changes from a perfect circle to an upright trapezoid in which the cross-sectional area of the outer half of the bend is large. . The cross section of the intake passage in the downstream curved portion 52 is shown in FIG. 13 (XI in FIG. 3).
II-XIII sectional view), FIG. 14 (XIV-XIV sectional view in FIG. 3), FIG. 15 (XV-XV sectional view in FIG. 3), FIG. 16 (FIG. 3
As shown in (XVI-XVI cross-section) in the figure, after it smoothly changes from an upright trapezoid to an inverted trapezoid with a large cross-sectional area of the outer half of the bend, it smoothly changes to a pair of inverted triangles after branching. There is.

Therefore, in the engine 1 of this embodiment,
In the intake stroke, when the piston 9 descends along with the rotation of the crankshaft 11, the intake main flow F is sucked into the combustion chamber 15 at a negative pressure through the path shown by the arrow in FIG. That is, when the intake mainstream 1 flows into the intake manifold 3 from the intake pipe 8 and is applied to the upstream curved portion 51, the intake mainstream 1 is separated from the central portion by the action of centrifugal force and gradually flows to the outer half side. At this time, as described above, since the cross section of the intake passage in the upstream curved portion 51 changes smoothly from a perfect circle to an upright trapezoid, the intake main flow F flows without resistance and the flow rate does not decrease.

Next, in the intake port 18 from the passage 50 in the intake manifold 3, when the upstream curved portion 51 is shifted to the downstream curved portion 52, the intake main flow F is gradually reduced by the action of the centrifugal force. It comes to flow on the outer half side. Also at this time, since the cross section of the intake passage in the upstream curved portion 51 changes smoothly from the upright trapezoid to the inverted trapezoid, the main intake air flow F flows without resistance and the flow rate does not decrease. Incidentally, in the fresh air, the fuel is injected from the fuel injection valve 31 at this time, and the intake main flow F separated into the mixture layer and the air layer by the partition wall 35 is then bifurcated at the downstream curved portion 52. However, since the cross section of the intake passage is also an inverted triangle here, the flow rate is maintained, and the combustion chamber 15 flows from above the intake valve 16 via the straight portion 53.
Flows into. As a result, a large amount of intake main flow F is sucked into the combustion chamber 15, and strong tumble flows Fm and Fa are generated.

In other words, in the downstream portion of the intake port portions 19 and 20, the upper half portion is wider than the lower half portion, so that the intake main flow F also passes and the flow rate is increased. The half part is naturally larger than the lower half part. On the other hand, when the intake valve 16 is opened, as shown in FIG. 8, the component a of the flow that increases the tumble flows Fm and Fa and the tumble flow F.
There is a flow component b that suppresses m and Fa. Therefore, in the downstream of the intake port portions 19 and 20, the flow rate in the upper half portion is larger than that in the lower half portion, so that the tumble flows Fm and Fa can be made stronger. Moreover, since the flow component a is in the same direction as the tumble flows Fm and Fa, the flow resistance to the flow component a is extremely small, and the flow rate as a whole can be greatly increased.

Further, as shown in FIGS. 7 and 8, a partition wall 35 is provided in the intake port 18 over substantially the entire length thereof. The partition wall 35 is provided so as to divide the inside of the left and right intake port portions 19 and 20 into two parts in the left and right direction, whereby the intake flow that has flowed into the intake port portions 19 and 20 is discharged to the central passage 33. It can be seen that it branches into the side passage 44.

That is, as shown in FIG. 14, the intake port 18 has the end face 6A of the cylinder head 6 which is the most upstream side.
In the vicinity, it is formed as one intake passage, and immediately thereafter, it is branched by the partition wall 35 into the central passage 33 and the side passage 34. Then, as shown in FIGS. 15 and 16, the central passage 33 is further divided into two near the central portion of the intake port 18. As a result, the intake flow flows into the combustion chamber 15 in a state of being branched into four when the intake valve 16 is opened.

The intake port 18 will be described in more detail with reference to FIGS. 7 and 8. As shown in FIG. 7, the intake port 18 has a substantially straight shape in order to direct the intake flow to generate the tumble flows Fm and Fa in the combustion chamber 15. On the other hand, due to the structure of the cylinder head 6, the axis of the intake opening opened / closed by the intake valve 16 and the direction of the intake flow cannot match. For this reason,
The substantial flow cross-sectional area in the straight line portion 53 is the smallest in the intake passage, and particularly near the downstream end of the intake port portions 19 and 20, the valve stem 16b and the stem guide 26 are provided.
The presence of the partition walls 35 significantly reduces the substantial cross-sectional area of flow.

Therefore, on the downstream side of the intake port portions 19 and 20, the bulge 55, which is shown by cross hatching in FIG.
56 are formed on the inside and outside thereof. As a result, a reduction in the substantial flow cross-sectional area in the straight portion 53 is prevented, and a sufficient flow rate is secured. Moreover, the bulge 5
5 and 56 are shown in FIG. 18 (XVIII-XVIII sectional view in FIG. 7)
As shown in FIG. 3, since the intake ports 19 and 20 are mainly provided in the upper half, the flow rate in the upper half is further increased, and stronger tumble flows Fm and Fa are generated.

Since the engine 1 of the present embodiment is constructed as described above, the intake flow sucked at the negative pressure from the intake port portions 19 and 20 in the intake stroke is shown in FIG. As shown in FIG. 17, a tumble flow Fm of air-fuel mixture and a tumble flow Fa of air are formed in layers. Then, even when the compression stroke is entered, the layered tumble flows Fm, F
Although there is a, the tumble flows Fm and Fa gradually start to collapse as the piston 9 moves upward. However, even at this time, since a relatively rich air-fuel mixture exists around the spark plug 30, good ignition and combustion are performed. The subsequent combustion stroke and exhaust stroke are exactly the same as those of a normal engine.

As described above, in the engine 1 of this embodiment,
By supplying the rich air-fuel mixture in the vicinity of the spark plug 30 by the strong tumble flows Fm, Fa, good ignition can be obtained even with a lean air-fuel mixture as a whole.
It has become possible to reduce both harmful exhaust gas components and improve fuel efficiency. Further, as shown in FIG. 6, the squish S generated by the valve recess 45 formed in the raised portion 44 on the upper surface of the piston 9 in cooperation with the ceiling surface of the combustion chamber 15.
Since F causes minute turbulence in the air-fuel mixture to increase the combustion speed after ignition, the thermal efficiency of the engine 1 is improved.
If this squish SF is too strong, it inhibits the growth of flame kernels and has the opposite effect. Therefore, it is important that the distance between the valve recess 45 and the ceiling surface of the combustion chamber 15 is appropriately adjusted. . Further, the valve recess 45 is configured such that when the piston 9 reaches the top dead center, even if the intake valve 16 opens due to valve overlap, the piston 9 and the intake valve 1 are
It is configured so as to avoid interference with 6. Therefore, by further increasing the top dead center position of the piston 9, the compression ratio can be increased and the thermal efficiency can be improved.

As shown in the graph of FIG. 19, the partition wall 35 is provided in the intake port portions 19 and 20 to promote stratification, so that the engine 1 can be operated with a leaner air-fuel mixture. Here, the horizontal axis in the figure is the air-fuel ratio (A /
F), and the vertical axis is the NO _x emission amount and the Pi (illustrated average effective pressure) fluctuation rate. Lines a and c show the characteristics of the engine 1 in which the partition walls 35 are provided in the intake port portions 19 and 20, and lines b and d are provided with a normal tumble flow intake port portion without the partition wall 35. It shows the characteristics of the engine. Lines a and b relate to NO _x emission, and lines c and d relate to Pi fluctuation rate.

As shown in FIG. 19, in the engine 1 provided with the partition wall 35 (see line a), the A / F value is leaner than in the engine using the normal tumble flow (see line b). NO _x emissions peak. Further, it is possible to reduce the peak value of the NO _X emission amount itself. That is, the stratification of the tumble flows Fm and Fa in the combustion chamber 15 is promoted, so that the A / F value at which the NO _x emission amount peaks compared to the conventional engine moves to the lean side.

Lines c and d show the relationship between A / F and Pi fluctuation rate. Here, the Pi fluctuation rate is a criterion for judging the combustion stability of the engine, and Pi
If the fluctuation rate becomes large, the combustion of the engine will not be stable, resulting in an unpleasant operating state accompanied by torque fluctuations. The reference line e in the figure is generally the Pi fluctuation rate of the combustion stability limit at which operation can be performed without discomfort.

As shown in FIG. 19, in the engine 1 (see the line c) provided with the partition wall 35, the normal tumble flow is obtained with respect to the limit value of the Pi fluctuation rate at which the stable combustion state in the cylinder is obtained. It is possible to operate with an A / F that is leaner than the engine that uses the engine (see line d).
O _X emissions can be greatly reduced. That is,
This shows that a stable combustion state can be obtained even with a leaner A / F, and the A / F at the combustion stability limit is improved.

Therefore, with this structure, it is possible to realize an engine which has extremely low fuel consumption and emits almost no NO _x . Furthermore, since the thickness t of the partition wall 35 is smaller than the diameter d of the valve stem 16b and the center line of the partition wall 35 and the axis of the valve stem 16b are aligned, the wall surface of the partition wall 35 on the side of the central passage 33 is The wall surface of the valve stem 16b on the side of the central passage 33 is biased toward the side passage 34 side. Therefore, the fuel particles in the mixed air flow along the partition wall 35 in the central passage 33 are directed toward the spark plug 30 while being guided to the inner surface of the valve stem 16b, and are concentrated in the vicinity of the spark plug 30 to ignite. Is performed well, and the lean limit can be further increased.

Particularly, in this embodiment, FIG. 9 and FIG.
As shown in FIG. 5, the downstream side of the intake port portions 19 and 20 is formed in a substantially inverted triangular cross section, and the cross-sectional area of the upper half portion is large, so that a strong tumble flow is generated in the combustion chamber 15. It is possible to secure the flow coefficient when the engine is fully opened. Further, in this embodiment, the bulges 55 and 56 are provided in the straight line portion 53 having the smallest substantial flow cross-sectional area in the intake port portions 19 and 20, and the partition wall serving as the flow resistance is provided on the downstream side of the valve stem 16b. Since it is not provided, it is possible to further effectively generate the above-described strong tumble flow and secure the flow coefficient when the engine is fully opened.

Further, in the construction in which the partition wall is not provided on the downstream side of the valve stem 16b in the intake port portions 19 and 20,
As described below, there are great advantages in manufacturing. That is, if a partition wall is provided also on the downstream side of the valve stem 16b, a portion of the partition wall corresponding to the valve stem 16b needs to be drilled after casting, but since the wall thickness is thin, the partition wall may crack during drilling. . Further, since a cantilevered partition wall exists on the downstream side of the valve stem 16b in the intake port portions 19 and 20, there is also a problem that the strength is not preferable. However, in this embodiment, since there is no partition wall on the downstream side of the valve stem 16b as described above, such a problem can be avoided at all. Moreover, it has been confirmed that even if the partition wall does not exist on the downstream side of the valve stem 16b, the stratification is hardly affected, and a great advantage can be provided in manufacturing.

Here, FIG. 20 is a graph showing the relationship between the port cross-sectional area, the average tumble ratio (rotational speed of tumble flow / engine rotational speed), and the average flow coefficient (total flow rate). Here, the line a shows the relationship between the port cross-sectional area and the average tumble ratio, and the line b shows the relationship between the port cross-sectional area and the average flow rate coefficient. Shows the average tumble ratio and the average flow coefficient of the engine equipped with the intake port section, and the ● and ◆ marks are the intake port section 1 with the upper half being sufficiently large, respectively.
The average tumble ratio and the average flow coefficient of the engine 1 with 9, 20 are shown. As shown in this graph,
By enlarging the upper half portions of the intake port portions 19 and 20 to secure the port cross-sectional area, both the average tumble ratio and the average flow coefficient can be improved.

As a result, the relationship between the tumble ratio and the flow coefficient is as shown in the graph of FIG. In this graph, the triangles indicate the engine using the conventional tumble flow,
The mark * indicates an engine in which the partition wall 35 is provided, but the partition wall 35 reduces the cross-sectional area of the intake ports 19, 20, and the mark * indicates the partition wall 35 and bulges 55, 56 of this embodiment. The engine 1 is shown. As shown in this graph, only by providing the partition walls 35 in the intake port portions 19 and 20, there is a problem that the flow coefficient becomes low even if the stratification of the intake flow is promoted, and the full-open performance deteriorates. Here, as shown by the asterisk, both the tumble ratio and the flow coefficient can be improved by making the upper half portions of the intake port portions 19 and 20 sufficiently large. In this way,
By compensating for the decrease in the cross-sectional area of the intake port portions 19 and 20 due to the partition wall 35, it becomes possible to generate a strong tumble flow and to secure the flow coefficient at the time of full opening of the engine.

FIG. 22 is a graph showing the torque and output of the engine. Lines a and c in the figure show the characteristics of the engine 1 of this embodiment, and lines b and d show the conventional intake port structure. It shows the characteristics of the engine with.
First, the lines a and b show the relationship between the engine rotation speed and the torque, but there is almost no difference between the two, and even if the engine 1 of this embodiment is operated with a leaner mixture than before. It can be seen that the torque equivalent to that of the conventional engine is realized. Lines c and d show the relationship between the engine speed and the output, but there is almost no difference between the two, and the engine 1 of this embodiment is operated with a leaner air-fuel mixture than before. It can be seen that also achieves the same output as the conventional engine. Thus, the engine 1 of the present embodiment
Then, by increasing the tumble ratio and the flow coefficient of the intake port portions 19 and 20, it was possible to realize torque and output equivalent to those of the conventional engine.

As described above, in the engine 1 of this embodiment, the partition walls 35 are provided in the intake port portions 19 and 20, and further,
By forming bulges 55 and 56 in the straight line portion 53 on the downstream side and sufficiently increasing the upper half portion, stable combustion can be performed with a leaner air-fuel mixture than a conventional engine without reducing both torque and output. Could be kept. As a result, it has become possible to achieve both high levels of reduction of NO _X and improvement of fuel efficiency.

Next, a modification of the piston is shown in FIG.
FIG. 24 (a view on arrow XXIV in FIG. 23), FIG. 25 (in FIG. 23)
XXV arrow view). As shown in these figures, in this modification, a pair of left and right curved portions 41, 42 are formed on the top surface 40 of the piston 9 from the exhaust side toward the intake side. Both the curved portions 41, 42 smoothly rise toward the intake side and form a raised portion 44 raised from the reference plane 43 of the piston 9. Therefore, the tumble flows Fm and Fa are generated by the curved portions 41 and 42 and the raised portion 44.
While being stratified, the piston 9 is guided from the top surface 40 of the piston 9 to the intake bore inner wall surface of the cylinder bore 12a. The rear surface of the raised portion 44 forms a valve recess 45 for the intake valve 16, while, as shown in FIG. 24, in the vicinity of the top dead center of the compression stroke, the ceiling surface of the combustion chamber 15 (the intake side sloped surface). The squish SF that disturbs the tumble flows Fm and Fa is generated in cooperation with 13).

On the other hand, when a virtual plane FD (indicated by a chain double-dashed line in FIG. 5) including the cylinder axis LC and orthogonal to the virtual plane FC is set, this virtual plane FD is formed between the curved portions 41 and 42. A center rib 46 is formed along the. The center rib 46 expands from the exhaust side toward the intake side at a predetermined angle, and distributes the tumble flows Fm and Fa to the left and right. Further, the center rib 46 has a triangular upper end flat surface portion 47 defined by the curved portions 41 and 42 and the valve recess 45. The cylinder axis LC penetrates the upper end flat portion 47, and the upper end flat portion 47 and the ignition plug 30 face each other near the top dead center as shown in FIGS. 24 and 25.

In the engine 1 of this modified example, the intake flow sucked by the negative pressure from the intake port portions 19 and 20 in the intake stroke is the tumble flow of the air-fuel mixture in the combustion chamber 15 as shown in FIG. Fm and the tumble flow Fa of air are formed in layers. Next, although the stratified tumble flows Fm and Fa are present even after shifting to the compression stroke, the tumble flows Fm and Fa start to gradually collapse as the piston 9 moves upward.
Then, when the piston 9 reaches the vicinity of the compression top dead center, both tumble flows Fm and Fa are distributed to the left and right by the center rib 46 formed on the top surface 40 thereof, and a large flow does not occur around the ignition plug 30. Further, at the time of ignition, as shown in FIGS. 24 and 25, the upper end flat portion 47 of the center rib 46 faces the ignition plug 30, and the flow that disturbs the ignition flows near the ignition plug 30. It almost disappears. Even at this point in time, since the rich air-fuel mixture exists around the spark plug 30, good ignition and combustion are performed. The subsequent combustion stroke and exhaust stroke are exactly the same as those of a normal engine.

As described above, in the engine 1 of the modified example, the rich tumble flow Fm, Fa supplies a rich air-fuel mixture in the vicinity of the ignition plug 30, and the center rib 46 formed on the piston 9 causes the ignition plug 30 to ignite.
Since the flow in the vicinity is suppressed, good ignition can be obtained even with a lean mixture as a whole.
It has become possible to reduce both harmful exhaust gas components and improve fuel efficiency.

Although the description of the specific embodiment has been completed, the embodiment of the present invention is not limited to this embodiment. For example, in the above embodiment, the cross-sectional shape of the curved portion is trapezoidal or triangular, but the cross-sectional shape of the bent outer half portion and the inner half portion may be semicircular or rectangular, and the cross-sectional area may be changed. The curved portion is not limited to two places. Further, the present invention may be applied to a three-valve engine having two intake valves and one exhaust valve, or may be applied to one having no partition wall in the intake port.

[0055]

As described above in detail, according to the internal combustion engine of claim 1 of the present invention, the cross-sectional area of the bending outer half portion of the bending portion is set larger than that of the bending inner half portion. By the centrifugal force, the main intake air near the outer half of the bend flows smoothly. Therefore, the reduction of the flow coefficient is prevented,
A strong tumble flow is generated, the lean burn limit is improved, and harmful exhaust gas components are reduced and fuel consumption is improved.

According to the internal combustion engine of the second aspect, in the case where the straight line portion communicating with the combustion chamber is continuous downstream of the plurality of curved portions, one half of the straight line portion continuous with the outer half portion of the curved portion is provided. Since the cross-sectional area was made larger than the cross-sectional area of the other half continuous with the inner half of the curved part, the main intake air flowing through the outer half of each of the multiple curved parts smoothly flows into the combustion chamber even in the straight part. Inflow, and a stronger tumble flow is generated.

Further, according to the internal combustion engine of the third aspect, since the boundary between the curved portion and the straight portion on the downstream side is located in the intake port, the space for the intake manifold is small like the V-type engine. On the other hand, the curved portion can be provided without difficulty, and the degree of freedom in design is improved. Further, according to the internal combustion engine of the fourth aspect, in the V-type engine, the curved portion on the upstream side is formed along the virtual plane that divides the V bank into two substantially equal parts, so that the shape of the intake passage is symmetrical in both banks. This makes it possible to prevent problems due to intake imbalance.

[Brief description of drawings]

FIG. 1 is a rear view of a V-type engine adopting the present invention.

FIG. 2 is an enlarged perspective view of a II part in FIG.

FIG. 3 is a view on arrow III in FIG.

FIG. 4 is a view on arrow IV in FIG.

FIG. 5 is a perspective view of a piston.

FIG. 6 is a vertical sectional view of a piston.

FIG. 7 is a vertical sectional view of an intake port.

FIG. 8 is a plan view of an intake port.

9 is a sectional view taken along line IX-IX in FIG.

10 is a sectional view taken along line XX in FIG.

11 is a sectional view taken along line XI-XI in FIG.

12 is a sectional view taken along line XII-XII in FIG.

13 is a sectional view taken along line XIII-XIII in FIG.

14 is a sectional view taken along line XIV-XIV in FIG.

15 is a sectional view taken along line XV-XV in FIG.

16 is a sectional view taken along line XVI-XVI in FIG.

FIG. 17 is an explanatory diagram showing a tumble flow generating action of the embodiment.

18 is a sectional view taken along line XVIII-XVIII in FIG.

FIG. 19 is a graph showing the effect of the intake port structure of the example.

FIG. 20 is a graph showing the effect of the intake port structure of the example.

FIG. 21 is a graph showing the effect of the intake port structure of the example.

FIG. 22 is a graph showing the effect of the intake port structure of the example.

FIG. 23 is a perspective view showing a piston of a modified example.

FIG. 24 is a view on arrow XXIV in FIG. 23.

FIG. 25 is a view taken along the line XXV in FIG.

FIG. 26 is a schematic perspective view showing a conventional stratified combustion internal combustion engine.

FIG. 27 is a schematic sectional view showing a conventional stratified combustion internal combustion engine.

[Explanation of symbols]

 1 Engine Body 2 Intake Manifold 3 Left Branch of Intake Manifold 6 Cylinder Head 8 Intake Pipe 9 Piston 12 Cylinder Bore 13 Intake Side Slope 14 Exhaust Side Slope 15 Combustion Chamber 16 Intake Valve 16b Valve Stem 17 Exhaust Valve 18 Intake Port 19, 20 Intake Port Reference numeral 22 Exhaust port 30 Spark plug 31 Fuel injection valve 33 Central passage 34 Side passage 35 Partition wall 40 Piston top surface 41, 42 Curved portion 44 Raised portion 45 Valve recess 46 Center rib 47 Upper end flat portion 51 Upstream curved portion 52 Downstream curved portion 53 Straight part 55,56 Swelling

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area F02M 35/10 101 E 35/104

Claims (4)

[Claims] 1. A stratified combustion internal combustion engine provided with an intake passage having a curved portion, wherein a cross-sectional area of an outer half of the bend in the curved portion is set larger than a cross-sectional area of an inner half of the bend. Combustion internal combustion engine. 2. A plurality of the curved portions are formed, a straight portion which is connected to the combustion chamber in a substantially straight line is formed downstream of the curved portion on the downstream side, and is further connected to an outer half portion of the curved portion. 2. The layered combustion internal combustion engine according to claim 1, wherein the cross-sectional area of one half of the straight portion is set to be larger than the cross-sectional area of the other half continuous with the inner half of the curved portion. 3. The stratified combustion internal combustion engine according to claim 2, wherein a boundary between the curved portion on the downstream side and the straight portion is located in an intake port formed in a cylinder head. 4. A V type having an intake passage between V banks, wherein the upstream side of the curved portion is formed along an imaginary plane that divides the V bank into approximately two halves. 2. The stratified combustion internal combustion engine according to 2 or 3.